This invention relates to multi-speed transmissions having three planetary gear sets and five torque transmitting mechanisms and more particularly to a family of such transmissions wherein six forward speed ratios and one reverse speed ratio are provided.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft) transmissions were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978, U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000, and U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions, such as Polak, having six or more forward gear ratios, passenger cars are still manufactured with three and four speed automatic transmissions and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gear sets, two clutches and three brakes. The Koivunen patent utilizes six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and another reverse speed ratio. The Lepelletier employs three planetary gear sets, three clutches and two brakes to provide six forward speeds. One of the planetary gear sets is positioned and operated to establish two fixed speed input members for the remaining planetary gear sets.
It is an object of the present invention to provide an improved family of transmissions having three planetary gear sets that are selectively controlled to provide six forward speed ratios and one reverse speed ratio.
In one aspect of the invention, each planetary gear set has three members including a sun gear member, a ring gear member, and a planet carrier member. In another aspect of the present invention, each of the planetary gear sets may be of the simple or compound type. In yet another aspect of the present invention, an input shaft is continuously connected with one member of one of the planetary gear sets and an output shaft is continuously connected with one member of another of the planetary gear sets. In still another aspect of the present invention, a member of each planetary, not otherwise continuously connected, are interconnected by an interconnecting member. In yet still another aspect of the present invention, five torque transmitting mechanisms are incorporated in each family member and consist of two stationary-type torque transmitting mechanisms and three rotating-type torque transmitting mechanisms.
In a further aspect of the present invention, the stationary-type torque transmitting mechanisms are selectively connectable between otherwise non-continuously connected members of the planetary gear sets and a stationary housing of the transmission. In a yet further aspect of the present invention, at least one of the rotating torque transmitting mechanisms is selectively connectable between otherwise non-continuously connected members of the planetary gear sets. In a still further aspect of the present invention, the torque transmitting mechanisms are engaged in combinations of three to provide six forward speed ratios and one reverse ratio.
The family of transmissions defined by the present invention provides a plurality of low-content, low-cost, six speed mechanisms that require only three planetary gear sets and five selectively engageable torque transmitting mechanisms. These mechanisms offer several advantages over four and five speed counterparts including improved vehicle acceleration performance and improved fuel economy. Each of the planetary gear sets includes three members. A first member of the first and third planetary gear sets are connected with a transmission input shaft and a transmission output shaft, respectively. A second member of the first and third planetary gear sets and a first member of the second planetary gear sets are continuously interconnected by an interconnecting member that may be comprised of a plurality of components. A first of the torque transmitting mechanisms selectively connects a member of the first or second planetary gear sets with a stationary component of the transmission. A second of the torque transmitting mechanisms selectively connects another member of the second planetary gear set or a member of the third planetary gear set with the stationary component. A third of the torque transmitting mechanisms selectively interconnects a member of the first planetary gear set with a member of the second or third planetary gear set. A fourth of the torque transmitting mechanisms selectively interconnects a member of the second planetary gear set with a member of the first or third planetary gear set. A fifth of the torque transmitting mechanisms selectively interconnects a member of the first or second or third planetary gear set with another member of the first planetary gear set, the second planetary gear set, the third planetary gear set, the input shaft, or the output shaft. As previously mentioned, the five torque transmitting mechanisms are selectively engaged in combinations of three to establish six forward speed ratios and a reverse ratio between the input shaft and the output shaft. A variety of numerical speed ratios and ratio spreads can be realized by the judicious selection of the ring gear/sun gear tooth ratios of the planetary gear sets.